1. Field of Invention
The present invention relates to a pixel structure of a liquid crystal display device. More particularly, the present invention relates to a pixel structure of an in-plane switching liquid crystal display device.
2. Description of Related Art
Liquid crystal display (LCD) has so many advantages, including high picture quality, small volume, light weight, low driving voltage and low power consumption, that LCDs are widely applied in electronic products such as medium or small-sized portable televisions, mobile phones, videos, notebooks, monitors for desktop computers and projection-type televisions. Therefore, as time goes by, LCDs gradually replace present cathode ray tube (CRT) monitors.
To compete with CRT monitors, LCDs are developed in the trend of wide viewing angle and high speed of response. For example, the developed in-plane switching (IPS) liquid crystal display device just provides the advantage of wide viewing angle. In an IPS liquid crystal display device, the common electrode is disposed over the gate line and the data line to provide larger aperture ratio of the device, thereby increasing the brightness of the device.
Reference is made to FIG. 1, which is a top view of a pixel structure of a conventional in-plane switching liquid crystal display device. A gate line 11 is adapted for providing a voltage to a gate electrode 151 of a transistor 15, and a data line 12 is adapted for providing a voltage to a source electrode 152 of a transistor 15. A drain electrode 153 is electrically connected to a pixel electrode 13 and a capacitor 16. The capacitor 16 is adapted to keep the electrical charges. The electrical field generated between the pixel electrode 13 and the common electrode 14 induces the liquid crystal molecules filled in the IPS liquid crystal display device to rotate and therefore an image is displayed on the device.
Reference is made to FIG. 2A, which is a schematic, cross-sectional view taken along 2A—2A of FIG. 1. The data line 12 is disposed over the glass substrate 10. The common electrode 14 is disposed over the data line 12. An organic layer 18 formed over the dielectric layer 17 is used to increase a distance between the data line 12 and the common electrode 14, thereby decreasing the generated coupling capacitance between the data line 12 and the common electrode 14. Reference is also made to FIG. 3, which is a schematic, cross-sectional view taken along 3—3 of FIG. 1. The gate line 11 is disposed over the glass substrate 10. The common electrode 14 is disposed over the gate line 11. An organic layer 18 formed over the dielectric layer 17 is used to increase a distance between the gate line 11 and the common electrode 14, thereby decreasing the generated coupling capacitance between the gate line 11 and the common electrode 14. Generally, the organic layer is made of photocured acrylic type material. In the conventional IPS liquid crystal display device as shown in FIG. 2A and FIG. 3, the common electrode 14 is formed over the gate line 11 and the data line 12 for providing larger aperture ratio of the device. However, the generated coupling ratio between the data line 12 and the common electrode 14 seriously influences the rotation of the liquid crystal molecules in the display region. Please refer to FIG. 2B. The density of the electric field lines 19 between the data line 12 and the common electrode 14, particularly in the region 20, is high. Hence, if the generated coupling capacitance between the region 20 and the data line 12 could be prevented, the generated coupling capacitance between the data line 12 and the common electrode 14 can be significantly lowered. Likewise, in FIG. 3, the density of the electric field lines between the gate line 11 and the common electrode 14, particularly in the region 30, is high. Hence, if the generated coupling capacitance between the region 30 and the gate line 11 could be prevented, the generated coupling capacitance between the gate line 11 and the common electrode 14 can be significantly lowered.
Although U.S. Pat. No. 6,069,678 has provided a solution for an IPS liquid crystal display device manufactured from a top gate transistor. No solution is provided for an IPS liquid crystal display device manufactured from a bottom gate transistor. The IPS liquid crystal display device manufactured from a top gate transistor can merely lower the generated coupling capacitance between the common electrode and the data line, where the generated coupling capacitance between the common electrode and the gate line can not be lowered.